The advantages of typical two-stroke internal combustion engines, which include relatively higher power to weight ratio over a comparable displacement four-stroke engine and fewer moving parts, is offset by the following disadvantages:
Two-stroke engines typically cannot use a pressurised lubrication system and instead, oil is added to the air/fuel mixture to allow lubrication of the piston within the cylinder and the roller bearings on the crankshaft.
Thus two-stroke engines burn oil, accounting for unwanted pollution.
A lack of a pressurised lubrication system requires roller bearings on the crankshaft and con-rods which are able to operate in the oil/fuel mix, unlike cheaper and simpler slipper bearings. This requires a heavy and expensive crankshaft assembly, to permit roller-bearing fitment.
In a previous application AU2009238281, the present applicant has disclosed a twin cylinder two-stroke engine arrangement in which each cylinder is divided into upper and lower cylinder sections by a fixed separator plate, with each piston moving reciprocatingly in the upper section between the separator plate and the cylinder head.
While this arrangement has the enormous advantages of allowing an increased primary compression ratio, pressure lubrication of the piston and simpler and cheaper crankshaft construction to name but some, the transfer of gasses from their initial induction into the area between the separator plate and the underside of the piston, into the combustion chamber above the piston, was found to be less than optimum.
It is an object of the present invention to address or at least ameliorate some of the above disadvantages.
Notes    1. The term “comprising” (and grammatical variations thereof) is used in this specification in the inclusive sense of “having” or “including”, and not in the exclusive sense of “consisting only of”.    2. The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.